Hi Oualid,

In addition to the mindboggle data mentioned by Prof. Klein, you can also find labeled ground truth scans at https://www.nitrc.org/projects/ibsr/.  There are two groups of scans there: "IBSR_V2.0" are the best quality and "20 Normals" are older scans.  IBSR scans have been downloaded and use in hundreds of publications.  

The mindboggle and IBSR scans are available for immediate download at no cost.  There are even more expert-labeled scans available, and while they are not free, they are the highest quality available anywhere.  Please see: https://www.nitrc.org/projects/manuallabels/.  The payment for a subscription to Neuromorphometrics' ever-improving database of labeled scans goes toward increasing the number of labeled scans available in the subscription.  There are 63 scans currently available in the 2012 subscription with subject ages ranging from 5 through 96.  The 2013 subscription (available in 2014) will include additional test-retest scans (same subject scanned and labeled twice) along with 30 scans from the ADNI database!

Andy.

Complete disclosure: I founded Neuromorphometrics 15 years ago (today!)